The present invention is described in the German priority application No. 19 930 683.4, filed Feb. 7, 1999, which is hereby incorporated by reference as is fully disclosed herein.
The present invention relates to an additive and a process for corrosion inhibition on apparatuses for conveying and transporting hydrocarbons in oil production and processing.
In industrial processes in which metals come into contact with water or with oil/water two-phase systems there is the danger of corrosion. This danger is particularly pronounced especially in salt water systems as occur in oil production and processing processes. Without special additives for protecting the equipment used, exploitation of a deposit and processing of the oil are incomplete.
Although such corrosion inhibitors have long been known, they are in many respects still inadequate. Many products, for example amides/imidazolines obtained from fatty acids and polyamines, are too oil-soluble and, owing to the unfavorable partitioning, are present in the corrosive water phase only in low concentration. They are therefore not very effective as corrosion inhibitors.
FR-A-2 407 258 describes amides of carboxymethylated oligomeric polyethylene glycol monoalkyl ethers having the structure RO(CH2CH2O)nCH2CONR1R2, in which R is an aliphatic radical having 8-20 carbon atoms or a phenyl radical substituted by a C8-C12-alkyl radical and R1 and R2 are hydrogen or alkyl radicals having at least 3 carbon atoms, and their use as corrosion inhibitors, detergent additives or antipollution additives for fuels. However, these amides no longer have any free amino functions and are less effective than the product according to the invention.
It was the object of the present invention to provide corrosion inhibitors which offer good or improved corrosion protection and also have improved water solubility compared with the corrosion inhibitors of the prior art.
As has now surprisingly been found, amidoamines/imidazolines which are obtainable from the reaction of polyglycol ethercarboxylic acids with polyamines exhibit these properties.
The invention relates to compounds of the formula 1
R1xe2x80x94Oxe2x80x94(Axe2x80x94O)xxe2x80x94(CH2)yxe2x80x94R2xe2x80x83xe2x80x83(1)
in which
R1 is branched or straight-chain C4-C30-alkyl, C4-C30-alkenyl or C4-C30-alkylaryl,
A is C2-C4-alkylene,
x is an integer from 1 to 100,
y is 1, 2, 3 or 4 and
R2 is a radical selected from structures of the formulae 2 and 3
xe2x80x94COxe2x80x94NR3R4xe2x80x83xe2x80x83(2)

in which one of the radicals R3 and R4 is a hydrocarbon chain which has at least one free NH or NH2 group and the other radical is hydrogen or a hydrocarbon chain which has at least one free NH or NH2 group and R5 is hydrogen or a hydrocarbon chain which has at least one free NH or NH2 group.
The invention furthermore relates to the use of the compounds thus defined as corrosion inhibitors.
In a preferred embodiment, R1 is a C8-C24-, in particular a C12-C18-alkyl or alkenyl radical. R1 is an aromatic radical; thus, a phenyl radical with alkyl substitution of from 4 to 12 carbon atoms is preferred.
A is preferably an ethylene or propylene radical, in particular an ethylene radical. X is preferably a number from 1 to 30, in particular 2 to 15.
Y is preferably 1 or 2, preferably 1.
The substituent R2 must be a free primary or secondary amino group. In one embodiment, this can be effected by one of the substituents R3, R4 or R5 being hydrogen. If R2 is of the formula 2, R3 and R4 cannot simultaneously be hydrogen. If R2 is of the formula 3, R5 may be hydrogen.
The radicals R3/R4 or R5 may be hydrocarbon chains which contain at least one free primary or secondary amino group. In a preferred embodiment, said hydrocarbon chains comprise 1 to 10 primary and/or secondary amino groups. The hydrocarbon chains moreover preferably contain 1 to 30, in particular 1 to 20, carbon atoms. In addition to the nitrogen atoms which form the primary and/or secondary amino groups, the hydrocarbon chains can contain further heteroatoms. If they contain further heteroatoms, oxygen is preferred.
The compounds according to the invention, as defined above, can be prepared by condensation of ethercarboxylic acids having the structure R1xe2x80x94O(Axe2x80x94O)xxe2x80x94(CH2)yxe2x80x94COOH with polyamines having at least one primary or secondary amino function.
The parent ethercarboxylic acids can be prepared by known routes, either by reaction of C4-C30-alcohol or alkylphenol reacted with ethylene oxide and/or propylene oxide, preferably with ethylene oxide, and subsequent oxidation of the terminal CH2OH function of the carboxylic acid, or by alkylation with chloroacetic acid derivatives according to the Williamson ether synthesis. Suitable parent alcohols are C4-C30 fatty alcohols, such as butanol, isobutanol, pentanol, hexanol, n-octanol, dodecanol, tetradecanol, hexadecanol, octadecanol and fatty alcohol cuts of natural or synthetic origin, such as oleyl alcohol, stearyl alcohol, behenyl alcohol and oxo alcohols of various chain lengths. Also suitable are branched alcohols, such as 2-ethylhexanol, isononyl alcohol, isodecanol, isotridecanol or isooctadecanol, and alkylphenols having a C1-C12-alkyl radical, such as nonylphenol.
These alcohols are reacted with alkylene oxides, such as ethylene oxide, propylene oxide or butylene oxide or mixtures thereof, particularly preferably ethylene oxide, to give the corresponding glycol ether. The products are preferably reacted with
1-30 mol of alkylene oxide, preferably 2-15 mol of alkylene oxide.
The ethercarboxylic acid can be prepared from these alkylene glycol monoalkyl ethers by oxidation with atmospheric oxygen in the presence of catalysts or by oxidation with hypochlorite or chlorite with or without catalysts. Particularly preferred is the alkylation of the glycol ethers with chloroacetic acid derivatives, preferably with sodium chloroacetate and sodium hydroxide solution by the Williamson method. The free carboxylic acid is obtained from the alkaline alkylating mixture by acidification with mineral acid (hydrochloric or sulfuric acid) and heating above the cloud point and isolation of the organic phase. The amides or imidazolines according to the invention are prepared from these ethercarboxylic acids by heating with polyamines and distilling off water.
The molar ratio of ethercarboxylic acid to polyamine is chosen so that not all available nitrogen atoms are converted into amides, so that free amino groups are retained in the end product.
Suitable amines are alkylamines having at least 2 and not more than about 10 nitrogen atoms. Examples of these are ethylenediamine, 2-aminoethylethanolamine, propylenediamine, diethylenetriamine, dipropylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine and industrial cuts of these amines. Furthermore, cyclic polyamines such as aminoethylpiperazine, piperazine or bis(aminoethyl)piperazine or 3-morpholinopropylamine are suitable. The condensation of ethercarboxylic acid and polyamine can be carried out with and without catalysts, and the reaction temperature here is in the temperature range of 100-220xc2x0 C., preferably 140-200xc2x0 C. For better removal of the water of reaction, reduced pressure can be applied (down to about 1 mbar). This is necessary in particular when the desire is to achieve high contents of imidazoline in the end product. The products according to the invention are then obtained as yellowish to brown, clear oils.
The products according to the invention can be used alone or in combination with other known corrosion inhibitors. In general, the corrosion inhibitor according to the invention is used in an amount such that sufficient corrosion protection is obtained under the given conditions. Typical concentrations for use, based on 100% active substance, are 5-100 ppm, preferably 10-30 ppm. Mixtures of the products according to the invention with other corrosion inhibitors known from the literature, such as amidoamines and/or imidazolines obtained from fatty acids and polyamines and their salts, quaternary ammonium salts, oxyethylated/oxypropylated amines, amphoglycinates and -propionates or betaines, are also particularly suitable as corrosion inhibitors.